Vitreous material



i To all wham e't may concern:

Patented'Feb. 17, 1925.

;. -UNITED STATESPATENT OFF ICE.

FREDERICK G. KEYES, 0F CAMBRIDGE, AND CHARLES A. KRAUS, OF WORCESTER, MASSACHUSETTS, ASSIGNORS T0 ARTHUR A. NOYES, TRUSTEE, 0F PASADENA,

CALIFORNIA.

No Drawing. Continuation of application Serial No. 752,374, filed March 6, 1913. 1 filed October 13, 1920. Serial No. 416,699.

Be it known that we, FREDERICK G. Knrns and CHARLES A. KnAUs, both citizens of the United States of America, residing at, respectively, Cambridge, Middlesex County, Massachusetts, and \Vorcester, \Vorcester County, Massachusetts, have invented certain new and useful Improvements in Vitreous Material, of which the following is a full, clear, and exact description.

Our invention consists in a new and useful composition of matter, and its object is the production of a vitreous material combining a low coefficient of expansion with a relatively low melting point and a low electrical conductivity at elevated temperatures.

Heretofore in the manufacture of a vitreous material of very low coefiicient of expansion, fused silica has been the only material available. This material, while possessing the valuable property of a low coefficient of expansion, possesses such physical properties at or near its melting point that it is exceedingly diflic'ult to manufacture a flawless product. Furthermore, its melting point lies at such an elevated temperature that it cannot be employed for many purposes where otherwise it would prove very valuable. or example, its melting or softening point lies above the point at which platinum melts and it is therefore impossible to effect a seal betweenplatinum and fused silica.

Attempts have been made to qualify silica by adding to it various other ingredients. In doing this, basic materials have been added, the basic material having either been added in a free state, in which case combination with'the free silica results in the mix- 40 ture, or otherwise, the basic material has been added in combination with an acid material, together forming a neutral salt or compoun The presence of basic material,

. even in relatively small quantities, imparts to the glass certain properties which it is desirable to avoid. Such glasses, for example, exhibit a relatively high coefficient of expansion with a relatively slight lowering of the melting point. At the same time, the

presence of the basic oxide, which is eitheradded in the form of a otherwise forms a bining with silica salt or compound or salt or, compound by com- (SiO or other acid constituent, greatly increases the conducting" VITREOUS MATERIAL.

This application power of theresulting mixture for the electric current. When a material is to be sub jected to yoltage stress particularly at elevated temperatures, it is desirable to maintain the insulating power of the material at the highest possible point.

We have found that anhydrous boric acid (B 0 may be added to and uniformly and homogeneously mixed with silica to form a stable and useful vitreous product. Such a product has a very low coeflicient of ex pansion, and at the same time, has a melting pointsufiiciently low to make it possible to carry out with it operations which are impossible with fused silica. A mixture of 20 per cent of boric acid with 80 per cent of silica may be sealed directly to fused silica tubes in a permanent and effective manner. At the same time, the melting point of this glass is sufficiently low to permit of its being sealed to platinum. Owing to the fact that a vitreous material of this composition contains no basic oxide, it possesses a relatively high insulating power under high dielectric strength, particularly at somewhat elevated temperatures.

It will be understood that if desired, small amounts of other oxides than anhydrous boric acid (B 0 may be added to silica (SiO as for example for coloring the mixture, without departing from our invention. In all cases, however, the mixture should compose a large excess of acid constituents (SiO and B 0 over basic constituents.

The vitreous composition is made by mixing silica (SiO and boric acid (B 0 in the form of a fine powder. After thorough mixing, the mixture is heated to a point where the two constituents intermingle and a homogeneous product results. The resulting melt may thereafter be worked after the customary manner of working glass, as for example, it may be drawn, blown, and the like, which operations are well understood by those skilled in the art.

The ease with which the resulting glass may be melted depends on the amount of anhydrous boric acid (13 0,) added. A composition comprising 80 per cent of silica ($0,) and 20 per cent of anhydrous boric acid (B 0 yields a product which we have found particularly useful in making seals for vapor electric a paratus constructed of fused silica. The uidity or fusibility of the said composition is great enough to permit its being applied to platinum tubes, while its coefficient of expansion is still sufficiently low to permit its being joined gr directly to fused silica. Such unctions between the said composition and fused silica have been tested by plunging them while. red hot into water without impairment of the junction. Such a glass is also useful in the construction of vapor electric apparatus intended to operate at an elevated temperature, since even at a red heat it possesses a high insulating power owing to the absence of basic constituents. Its melting point, moreover, may be made sufiiciently'high so that it will not give way to mechanical stress at elevated temperatures. As a substltute for fused quartz it possesses many advantages, since it may be worked through a large temperature range. Our invention completely or in large part the acid constituents (SiO and (B 0 present.

It is to be understood that in compounding glasses, the same product results whether a basic and an acid constituent be added separately or whether they be added in the same proportions in the combined form.

This application is a continuation of our application Serial 752,374, filed March 6,1913.

By the use of the term a. coefficient of expansion in the neighborhood of that of silica in the claims we refer toany vitreous material having a coeflicient of expansion approximating that of silica, which is practically zero, and less than that of the glasses otthe prior art, glasses having such intermediate coeliicients being described in our Patent No. 1,014,757. dated January 18,

What we claim is:

1. A 'glass having a coeilicient of expan' sion in the neighborhood of thatof silica and greater than that of silica.

2. A glass having a coeflicient of expansion in tlieneighborhood of that of silica and being more fusible than silica.

3. A vitreous material composed of silica qualified by boric anhydride.

' 4. A vitreous material composed of silica and boric anhydride substantially in the proportion of four'parts of silica to one part of boric anhydride.

5. A vitreous material comprising the ox ides of silicon and boron, the material hav- 'in a coetlicient of ex ansion in the nei hborhood of that of silica.

6. A vitreous material comprising the oxides of silicon and boron, the material having a coeflicient of expansion in the neighborhood of that of silica and being more fusible than silica.

In testimony whereof we hereto afiix our signatures.

FREDERICK G. Kern s. CHARLES A. KRAUS. 

